As this type of boring tool, there is known a reamer disclosed, for example, in Patent Document 1 having a long cylindrical shank part rotated around an axis and an edge part formed on the tip of the shank part, in which a chip discharging groove extending axially to the rear end side is formed on the outer periphery of the edge part and a cutting edge is formed at a ridge part on the outer periphery at the tip of the wall face of the chip discharging groove facing forward in the tool rotating direction.
This reamer is used on attachment to a cutting tool disclosed, for example, in Patent Document 2. This cutting tool, which is attached to the main shaft end of a machine tool and the like, is rotated axially and also inserted into a pilot hole of a workpiece, for example, a stem guide hole, a valve hole on the cylinder head of an engine and the like, thereby cutting the inner wall face of the pilot hole to form a bored hole having a predetermined inner diameter.
FIG. 20 shows an example of a method in which a conventional reamer is used to bore a pilot hole. Further, FIG. 21 and FIG. 22 show an example of a conventional reamer.
A reamer 1 is constituted with a shank part 2 formed in a long cylindrical shape and an edge part 3 arranged at the tip of the shank part 2, as shown in FIG. 22.
The shank part 2 is made of a steel product and formed approximately in a multi-staged cylindrical shape. An attachment part 4 for attaching the reamer 1 to a cutting tool is provided on the rear end side thereof. A V-shaped groove 5, the center of which is recessed toward the rear end side of the shank part 2, is formed on the tip face of the shank part 2.
A coolant supplying port (not illustrated) is formed at the shank part 2 so as to penetrate through from the tip of the shank part 2 to the rear end side and thus opened on the V-shaped groove 5.
The edge part 3 is constituted with cemented carbide and formed approximately in a cylindrical shape. A raised part 6, which can be fitted into the V-shaped groove 5 formed on the tip face of the shank part 2, is formed on the rear end face thereof.
As shown in FIG. 21 and FIG. 22, six rows of chip discharging grooves 7 extending to the rear end side in the axis O direction and twisted at a predetermined angle forward in the tool rotating direction T, are arranged at the tip on the outer periphery of the edge part 3 peripherally at equal intervals in rotational symmetry every 60 degrees with respect to the axis O. In this instance, as shown in FIG. 22, a length of the chip discharging groove 7 in the axis O direction, S, is made shorter than a length of the edge part 3 constituted with cemented carbide in the axis O direction, L.
A cutting edge 10 is formed at a crossed ridge part between the wall face 8 of the chip discharging groove 7 facing forward in the tool rotating direction T and the outer peripheral face 9 continuing to the backside in the tool rotating direction T. In the thus formed cutting edge 10, the wall face 8 of the chip discharging groove 7 facing forward in the tool rotating direction T is provided as a cutting face, while the outer peripheral face 9 continuing to the backside in the tool rotating direction T is provided as a relief face.
As shown in FIG. 21, the chip discharging groove 7 is formed so as to provide a V-shaped cross sectional face, with the groove bottom formed in a recessed circular arc shape, and an angle formed by the V-shape is to be approximately 80 degrees. The wall face 8 facing forward in the tool rotating direction T as a cutting face is formed in such a manner as to extend radially approximately along a circle formed by the outer cross section of the edge part 3. Further, a communicating port (not illustrated) extending along the axis O and opened on the rear end side (raised part 6) is formed in the vicinity of the edge part 3 in the axis O direction. An ejection port 11 is formed extending from the communicating port to each of the chip discharging grooves 7 and opened at the groove bottom part.
Further, a back tapered part 12, which reduces in diameter gradually from the tip side to the rear end side, is formed at the edge part 3. As shown in FIG. 22, a length of the back tapered part 12 in the axis O direction, B, is made shorter than a length of the chip discharging groove 7 in the axis O direction, S. In other words, the length of the back tapered part 12 in the axis O direction, B, the length of the chip discharging groove 7 in the axis O direction, S, and the length of the edge part 3 in the axis O direction, L, are related to be L>S>B.
The reamer 1 is not only attached to a cutting tool and rotated around the axis O but also carried to the tip side in the axis O direction and inserted into a pilot hole formed on a workpiece W beforehand, thereby cutting the inner wall face of the pilot hole. On this cutting process, since the chip discharging groove 7 is formed so as to be twisted forward in the tool rotating direction, chips generated by the cutting edge 10 are consequently guided to the tip side of the reamer 1. Further, coolant is ejected via a coolant supplying port and a communicating port from an ejection port 11, by which the chips are discharged to the tip side of the reamer 1 in such a manner as to be flowed by the coolant flowing through the chip discharging groove 7.
Then, as shown in FIG. 20, in a conventional method of boring a pilot hole, the reamer 1 in which a length of the edge part 3, L, is longer than a length of the pilot hole, H, is used to bore the pilot hole. As a result, the edge part 3 of the reamer 1 is arranged so as to penetrate through a bored hole formed by boring the inner wall face of the pilot hole.
In the above-described reamer, a coolant supplying port for supplying coolant to the edge part is formed at a shank part so as to penetrate through the shank part, and a communicating port communicatively connected to the coolant supplying port and an ejection port extending from the communicating port to the groove bottom part of the chip discharging groove are formed at the edge part.
Coolant is ejected from the ejection port via the coolant supplying port and the communicating port, by which the coolant is supplied to a pilot hole of a workpiece to reduce the cutting resistance when the cutting edge formed at the edge part cuts into the inner wall face of the pilot hole. As a result, not only is chatter of the reamer suppressed to accurately form a bored hole but also early wear of the cutting edge is suppressed to provide an increase in the life of the reamer.
Further, an edge part at which the cutting edge is formed is constituted with hard cemented carbide, and the edge part constituted with the cemented carbide is jointed by soldering at the tip of a steel-made shank part to provide a reamer, or a shank part is made of cemented carbide and sintered integrally with the edge part to provide a reamer (refer to Patent Document 1).
In these reamers, an edge part constituted with hard cemented carbide is used to cut the inner wall face of a pilot hole formed on a workpiece, thereby wear resistance is improved to provide an increase in the life of the reamers.    PATENT DOCUMENT 1: Japanese Unexamined Patent Application, First Publication No. 2000-263328    PATENT DOCUMENT 2: Japanese Unexamined Patent Application, First Publication No. 2002-59313